This invention relates to a method and a system for accurately identifying at least one geometrical transformation applied to an image that has two dimensional waves embedded therein, whenever such an image has been subjected to the geometrically transformation.
It is already known in the art that rotation of a space causes distribution of a frequency domain (Fourier Transformed Space) to be rotated as well. While E. De Castro and C. Morandi (IEEE Trans. Pattern Analysis and Machine Intelligence, Vol. PAMI-9, No. 5, pp. 700-703, 1987) apply this principle to geometrical correction (geometrical registration) of a rotated image, nevertheless they do not propose or suggest intentionally embedding two dimensional waves. Rather, they use a method of repetitively searching for a rotational angle that will maximize a correlation in a frequency domain between an original image and a rotated image. Thus, this method inevitably requires use of an original image for the purpose of determining any linear transformations applied thereto.
U.S. Pat. No. 5,636,292, entitled xe2x80x9cSteganography Methods Employing Embedded Calibration Dataxe2x80x9d, discloses a digital watermarking method for embedding a multi-bit identifying function in a two dimensional pattern itself. In this patented invention, information signals, to be embedded as digital watermarks, and other information signals, to be used for discerning any deformation applied to an image, are integrated together; and, in the case of embedding a pattern consisting of a plurality of two dimensional waves, the embedding pattern is rendered to have at least one axis of symmetry. However, with such symmetry, a linear transformation at the time of pattern extraction has a plurality of solutions and, thus, there is no way to completely identify the geometrical transformation. Further, this patented invention uses a method steps of: transforming an image that has a two dimensional wave pattern embedded therein to another space (frequency domain); filtering; and, returning the same to a real domain again. However, in accordance with such a method, it is difficult to control invisibility and/or degradation of image quality. Digital watermarks embedded in an image for copyright protection require countermeasures against any manipulations for removing them. Such manipulations for removing digital watermarks include geometrical transformations such as clipping, rotation, scaling, anisotropic scaling, and the like. However, to the best of our knowledge, the prior art fails to provide a single means for rapidly and accurately identifying geometrical transformations applied to an image, which contains these digital watermarks therein, and correcting the same.
Moreover, where a manufacturing process requires accurate position control of a manufacture piece, the prior art fails to provide any means for allowing additional position control to be performed whenever the manufacture piece is geometrically deformed due to any changes in an external environment.
Accordingly, it is an object of this invention to provide a method and system that are capable of easily and rapidly identifying at least one geometrical transformation applied to an image in a accurate manner without using its original image.
Also, it is another object of this invention to provide a method and system for embedding two dimensional waves in an image, thereby to easily control invisibility and/or degradation of image quality.
Also, it is another object of this invention to provide a method and system that are capable of accurately and rapidly identifying at least one geometrical transformation applied to an image that contains digital watermarks therein.
Also, it is another object of this invention to provide a method and system that are capable of accurately and rapidly detecting at least one geometrical transformation applied to an original image even where a digital watermarking image is subjected to clipping, rotation, scaling, anisotropic scaling, or the like.
Further, it is yet another object of this invention to provide a method and system for reading at least one geometrical transformation applied to a manufacture piece, which requires accurate position control, and performing appropriate position control of the manufacture piece.
These and other objects are realized by the a geometrical correction system of this invention which comprises creation of at least one pattern consisting of asymmetric two dimensional waves, embedding at least one pattern consisting of asymmetric two dimensional waves in a real domain, and calculation of at least one geometrical transformation applied by way of extraction of the embedded two dimensional waves. Firstly, said creation of At least one pattern consisting of asymmetric two dimensional waves means to calculate a two dimensional wave parameter set for creating at least one pattern adapted for use in the geometrical correction system of this invention. Secondly, said embedding of at least one pattern consisting of asymmetric two dimensional waves in a real domain means to add the pattern to an original image. Finally, said calculation of at least one geometrical transformation applied by way of extraction of the embedded two dimensional waves means to calculate parameters of the embedded two dimensional waves from the image that is subjected to at least one geometrical transformation, to compare these parameters with the two dimensional wave parameter set of the embedded pattern, thereby to identify the geometrical transformation applied to the embedded image.
Also, this invention comprises a digital watermarking system that makes use of the foregoing method and system in a way to improve robustness to a geometrical transformation. More particularly, this invention comprises a method and a system for intentionally embedding a number of two dimensional waves in an image, whereby at least one geometrical transformation applied to the image may be rapidly and accurately identified through calculations of such information about how magnitudes of periods and directions of the embedded two dimensional waves have been transformed. According to this invention, this is accomplished without requiring use of an original image that is free of the embedded two dimensional waves.